Fish Tank Filters: Which One Should You Get?

What do most people think when they hear you keep pet fish? They probably conjure up memories of their great aunt’s dirty goldfish tank, covered in mystery slime and reeking of stagnant swamp water. But you and I know the secret to having a beautiful aquarium with crystal clear water… clearly, we just need to find the perfect fish tank filter!

Why do Aquariums Need Filtration?

As one of the key components of an aquarium, filtration is responsible for moving and cleaning the tank water, making it safe for fish to live in. The three main types of filtration are mechanical, biological, and chemical filtration. Some filters work better than others. Here’s an overview:

Mechanical filtering uses sponges and filter socks. Filter floss pads are used to physically strain out any debris in the water. This is similar to a coffee filter. Mechanical filtration acts as a garbage can that collects trash – which means you as the fish owner are still responsible for cleaning the filter media (in other words, “emptying” the trash can before it overflows). – Biological filtration uses beneficial bacteria or aquarium plants that can consume the toxic ammonia and nitrogen compounds that result from your fish’s waste. Beneficial bacteria grows on any surface, including the walls and gravel in your aquarium, so many filters come with biomedia or bio-rings with high surface area to provide more places for the bacteria to live. – Chemical Filtration uses activated Carbon or special resins that can remove medication, tannins, as well as other impurities. Once the chemical filtration becomes saturated with impurities, the media is no longer able to absorb pollutants from the water

Examples of mechanical, biological, and chemical filter media

Bottom Line: mechanical filtration makes your water clearer, biological filtration makes your water safer, and chemical filtration is something best saved for removing impurities from the water.

What are the Most Popular Types Of Filters?

Now that you’re familiar with what filtration does for an aquarium, let’s talk about the actual equipment you can purchase (in rough order of most to least common).

Sponge filter

Aquarium Co-Op sponge filters

The most basic filter requires at least three components. A sponge filter, which sits inside the tank, an air pump (which is outside the tank), as well as airline tubing to link them. The sponge filter is hollowed by air pumps that push air through the tubing. The rising bubbles of air draw water through the sponge walls, thus mechanically collecting debris from the water and giving beneficial bacteria place to grow.

Pros: I could go on and on, but this device is cheap, easy to clean, and hard to break since it has very few mechanical parts. It is gentle enough to not eat fish fry, shrimps, or other slow-moving animals, but provides water circulation and surface movement. To prepare for an emergency, you can buy battery-operated pumps that will pump air to the sponge during power outages.

Cons: The sponge filter takes up physical space in the fish tank, so you may want to hide it behind a rock, plants, or other aquarium decor. Also, there’s no way to add chemical filtration if needed. I personally don’t like the bubbling sound from a sponge filter, but that’s easily remedied with a little air stone.

The bottom line: Sponge filter are a common item in fish shops, fish rooms and breeding facilities. They’re reliable and economical. Why not use what’s tried and true?

Hang-on-Back Filter

Hang-on-back filter for nano tanks

Just as the name describes, a hang-on-back filter sits on the top rim of an aquarium with the filter box hanging outside the tank and the intake tube lowered into the tank. Water is sucked up the intake tube via the filter’s motor, passed through all the media in the filter box, and then typically returned back into the aquarium like a mini waterfall.

Comments: I love that the filter media can be customized and you can use all three types of filters. Actually, a hang-on back filter does a better job at mechanical filtering than a sponge filter. It also allows you to add a fine filterpad to polish the water. The device is very simple to service since most of the media is outside of the aquarium, allowing you to easily remove the media for gentle washing. The AquaClear filter that I have has a variable flow rate. This allows me to adjust the water circulation according to my needs.

Cons: Because a power motor drives the water flow, there’s a chance it can burn out if the filter runs dry or accidentally sucks up sand (use a pre filter sponge to prevent the latter). Additionally, if you don’t like the waterfall sound, just raise the water level in your aquarium and you’ll barely notice the noise.

Summary: This filter was my first and still is in use today. As a popular staple in the freshwater aquarium hobby, the hang-on-back filter excels in all three arenas of filtration and has extremely flexible options for hot-rodding it to your tastes.

Canister Filter

A canister filter is essentially filtration in a plastic cylinder or box form factor that often sits under the tank, with intake and output hoses that reach into the aquarium. A motor pulls water into the canister. The water then travels through several filter media trays and is returned to fish tank.

Pros: Just like the hang-on-back filter, the canister filter takes up very little room inside the aquarium and is highly customizable. Some models include extra features such as an inline heating, UV sterilizer, or automatic priming. Many hobbyists consider it to be one of the best readymade filters on the market.

Cons Also, that nifty little canister is pretty difficult to service, requiring you to practically disassemble the whole setup every time you want to clean out the insides. Keep your towels handy as there is a higher chance of flooding during maintenance. Finally, because the filter media lives outside the aquarium in a closed box, there’s a greater risk of suffocating and killing off your beneficial bacteria during a power outage.

Summary: If your discus needs extremely clean water or you have an African cichlid aquarium with high bioloads, then this might be the right product for you. This premium product is worth the extra time and money.

Fluidized Bed Filter

Ziss moving bed filter, powered by an air pump

Traditionally, fluidized bed filters have been more of a DIY approach to filtration, but now there’s a compact, off-the-shelf version known as the Ziss Bubble Moving Media Filter. Water flows into a chamber of small media granules (like sand or plastic pellets), causing the media to swirl about like a fluid. The media’s constant contact of oxygenated water greatly increases bacteria growth.

Pros: The Ziss filter is air-driven like the sponge filter, so it has very few mechanical parts to break and provides plenty of surface agitation for increased gas exchange. It has a sponge prefilter on the bottom to prevent fry from being sucked up. This is also easy to remove for maintenance. As a device focused on biological filtration, it’s great for goldfish and turtle aquariums with high bioloads – and unlike sponge filters, the hard plastic is too hard for turtles to chomp through!

Cons: This filter is relatively tall at 11 inches, so it’s only suitable for taller tanks (not a 10 gallon or 20 gallon long aquarium). Like the sponge filter, it’s not as customizable for adding chemical filtration or more mechanical filtration. And I’d say the noise level is also comparable to a sponge filter (mostly coming from the bubbles and air pump itself).

The bottom line: A fluidized bed filter is a great way to improve your biological filtration. A single Ziss Bubble Bio filter can handle 20-40 gallons of water. It can also be used in conjunction with other filters.

Live Aquarium Plants

What filter should I get?

Ah, the golden question that every aquarist wants to know. First, I haven’t covered all the filters. Secondly, there’s no such thing as a one-size-fits-all “best” filter, but rather a wide variety of different tools that can best accomplish different tasks. You should consider the requirements of your aquarium, such as water circulation, stock levels, budget, and ease of use. Then, choose the best solution for you. Good luck and happy filter shopping!